The present invention relates to a data processing system and, more particularly, to a data processing system which has a storage configuration containing a main storage and an extended storage.
Conventional data processing systems with a storage configuration containing an extended storage in addition to a main storage is constructed by a system comprising an instruction processor (IP), a storage controller (SC), an input-output processor (IOP), a main storage (MS) and an extended storage (ES). The extended storage of the storage configuration in these data processing systems is positioned functionally in the same category as an external storage and considered as a device to carry out paging processes.
For instance, a data processing system with the extended storage of this type is disclosed in U.S. Pat. No. 4,476,524 corresponding to Japanese Patent Publication (laid-open) No. 9,276/1983. This data processing system is provided with a page transfer bus that is an independent data path between the extended storage (page storage) and the main storage and with a data transfer means. This system can realize a system configuration to transfer data between the extended storage and the main storage on the page transfer bus.
In data transfers between the main storage and the extended storage by a transfer instruction for transferring data, restrictions are placed on a unit of data to be transferred requiring that the minimum unit of data to be transferred be one page (4 KB (kilobytes)) and on a main storage address directed by the transfer instruction requiring that the address should be on the boundary of the page.
When the extended storage is intended to be used for purposes other than for the paging process in the data processing system with the extended storage, these restrictions on the minimum unit of transfer data of one page to be transferred between the main storage and the extended storage by the transfer instruction and on the location of the main storage address of an operand of the transfer instruction being on the boundary of the page present the following problems:
(1) In transferring data in an arbitrary amount of data to be transferred between the main storage and the extended storage, processing for transferring data can be executed between a data region and a work region on the main storage, for example, by a MOVE instruction. At this end, it is possible to provide the extended storage with the data region and the main storage with the work region to permit the data transfer between the extended storage and the main storage by means of a transfer instruction processing by the MOVE instruction. In order to implement a new program containing the transfer instruction for this processing, however, the minimum unit of 4 KB for the data transfer between the main storage and the extended storage by the transfer instruction suffers the disadvantage that a capacity in the regions of the main storage and the extended storage required by the program is increased.
(2) In modifying a conventional existing program, the existing program is designed such that, in both the data region and the work region, a majority of their addresses are a 4-byte boundary or a 8-byte boundary requiring that the program be modified to a great extent. Such a great modification of the program, however, is practically impossible.